1,3-dichloro-2-propanol (DCP) is a di-functional raw material that may be useful in various processes. It may be prepared by chlorination of glycerin (K. Kawahata, Y. Awano, Y. Hara, Japanese Patent Publication No. JP2010047492 (2010)), and is an intermediate in the production of epichlorohydrin, useful for the manufacture of epoxy resins, from glycerin (E. Van der Graaf, L. Gonclaves de Mendonca Filho, WO2010102368 (2010); D. Shi, X. Che, Z. Shen, Y. Song, L. Fu, P. Dong, J. Jin, Q. Zhou, B. Gao, Chinese Patent CN101805243 (2010); W. Fan, C. Kneupper, S. Noormann, R. Patrascu, B. Hook, C. Lipp, M. Cloeter, H. Groenewald, United States Patent Application No. 2010/029960 (2010)). As part of the isomeric mixture of 1,3-dichloro-2-propanol and 2,3-dichloro-1-propanol mixture obtained by chlorohydroxylation of allyl chloride with hypochlorous acid, reaction of DCP with base generates epichlorohydrin (M. Spadlo, A. Brzezicki, J. Dula, T. Wilusz, W. Madej, A. Gorzka, E. Oknińska, T. Koziel, J. Wasilewski, Polish Patent PL176853 (1999); D. Shi, Y. Song X. Che, P. Dong, B. Gao, Chinese Patent CN101712661 (2010)).
Reaction of epichlorohydrin with hydrogen chloride produces primarily DCP, with a trace of the 2,3-isomer and other by-products (M. Spadlo, M. Adamczyk, A. Brzezicki, J. Dula, K. Giza, A. Gorzka, W. Madej, G. Masztalerz, E. Oknińska, Z. Pokorska, M. Stajszczyk, Z. Zawiski, Polish Patent PL163256 (1994); H. Schmidt-Neuhaus, DE1210774 (1966)).
One low cost source of DCP is the distillation residue from a propylene oxide/propylene glycol process. Functionalization of propylene by hydrochlorination to generate propylene oxide and propylene dichloride also generates epichlorohydrin as a by-product. Following recovery of the epichlorohydrin and other products by distillation, a waste stream, often referred to as the Crude PDC Bottoms, remains. Although the accessible amount of epichlorohydrin has been recovered from this waste stream, it still contains residual epichlorohydrin and other by-products.
The residual epichlorohydrin in the Crude PDC Bottoms can be converted to DCP by reacting with hydrogen chloride. However, the isolation and purification of the DCP generated is difficult due to an azeotrope formation of DCP with 2,2′-oxybis(1-chloropropane), one of the major by-products of the propylene oxide/propylene glycol waste stream. An azeotrope is a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation, because when the solution is boiled, the vapor that results has the same ratio of constituents as the original liquid mixture. This may be because the boiling point temperature of the azeotrope is less than the boiling point temperatures of any of its constituents (a positive azeotrope) or because the boiling point temperature of the azeotrope is greater than the boiling point temperatures of any of its constituents (a negative azeotrope). Traditional heterogeneous azeotropic distillation requires an additional column for entrainer recovery. Alternative methods of conventional distillation are time-consuming and costly. A need exists, therefore, for a simplified and economic processes and apparatuses for isolating DCP from the 2,2′-oxybis(1-chloropropane)-containing Crude PDC Bottoms waste stream.